What would be the best way to get next and previous record?

Let’s say I have a class Post and I do a simple find for a record,
like Post.find(16). Given this AR instance what would be the best way
to get the previous and next records? I can’t just use ids (15, 17 in
this example) because records can be deleted.

Am I asking AR to do too much here and craft some custom SQL to handle
this?

Thanks for the help.
Mike

found it!

http://svn.viney.net.nz/things/rails/plugins/acts_as_ordered/README